Topic 11. Lambda expressions, functional interfaces, and the Stream API

Goal: learn to pass behavior, build lazy pipelines, group data, and handle the absence of a result explicitly.

Lecture contents

1. Functional interfaces — Functional interfaces and target types · Standard functional interfaces
2. Method references and Optional — Method references and comparators · Optional and the absence of a result
3. The Stream API pipeline — Source, pipeline, and terminal operation · Transformation and flattening · Terminal operations and reduction
4. Collectors and Gatherers — Collectors and grouping · Primitive streams and Gatherers
5. Parallelism and testing a pipeline — Parallelism, errors, and debugging · The pipeline contract and equivalence testing

Practice and review

• Practice — 3 worked examples with complete code
• Tasks — 30 variants, each with tasks at three difficulty levels
• Summary — conclusions, self-check questions, and useful links